GEOLOGICAL DISTRIBU 1 ION. 



39 



similar that there is no wonder that the fauna;' did not differ greatly. In the Laranm-, 

 as in the Judith River, there were Baenidae and I rionychidae. The Dermate- 

 mydidae are represented by at least one species, Basdemys sinuosa, not greatlv 

 different from B. variolosa of the Judith River. I he Pleurodira appear to be 

 represented by one species, Naiadochclys mgravata, from New Mexico. 



On entering the Tertiary there is no striking change in the turtle fauna. In the 

 Fort Union, the Puerco, and the Torreion, there are yet Trionychidae, Dermate- 

 mydidae, and Baenidae. Representatives of the same families pass up into tin 

 Wasatch. Here, however, new elements enter, the Emydidae and the lestudinukc. 

 It is not improbable that Gyremys spectabilis of the Judith River beds is an emvd, 

 but the group is unmistakably represented in the Wasatch by Echmatemys, a genus 

 in some respects highly specialized. 1 he Testudinidae are represented by the 

 genus Hadrianus, the oldest-known genus of the family. All these \\ asatch turtles 

 inhabited either the land or the fresh waters of streams. 



In the Atlantic region we have nearly contemporaneous deposits; and in them 

 we find fragmentary remains of a few probably marine turtles and of Trionychid;e. 



The Wind River beds have so far furmsht only a single species of Baptemys, and 

 the humerus, 187 mm. long, of a trionvchid. 



The Bridger beds of \\ voming are exceedingly rich in turtle remains, as thev 

 are also in the bones of crocodiles and mammals. The Baenidae were numerous in 

 species and individuals. Only 2 genera of dermatemyds have been found. Emy- 

 didae abounded, and Trionychidae ran riot. In addition to these there were a few 

 species of Plastomenidae. All together, there are 50 or more species of turtles 

 described from the Bridger Eocene. The abundance of Baenida.' and especially 

 of the Trionychidae shows that there were numerous streams and lagoons; and this 

 conclusion is confirmed by the presence of many species of crocodiles. The occur- 

 rence of the great turtle Hadrianus seems to indicate the proximity of dry land. 



Nearly all the species of Bridger turtles occur in the lower portion, that known 

 as level B. No turtles have yet been described from the limestone bands, but 

 fragmentary remains occur there. These bands appear to have been laid down in 

 shallow lakes. 



So far as known the turtles of the Uinta beds belong to genera found in the 

 Bridger beds. No Plastomenida? have been found, and the Baenida? appear for the 

 last time in our calendar. 



During the Oligocene epoch the scene, for the student of turtles, shifts from the 

 sea shore and the mountain regions to the Great Plains. In the lowest division, tin 

 Chadron or Titanotherium beds, are found 1 trionvchid, 1 dermatemyd, and 

 1 emvd, silent witnesses of the presence of streams. On the other hand, there were 

 numerous species of Testudinida?, or dry-land tortoises, some of wdiich attained a 

 large size. Of Stylemys nebrascensis great numbers of shells have been found in 

 South Dakota and Colorado, in the Brule clays, or Oreodon beds. Species of 

 Testudo were more abundant in the same deposits in Colorado. There can be no 

 doubt that at this time the climate of the Plains region had become arid and the 

 streams few. A similar climate appears to have prevailed in the John Day region 

 of Oregon, where 2 or 3 species of Stylemys abounded, but, so tar as known, no 

 other turtles. 



The Miocene deposits of the interior of the continent are characterized by the 

 presence of species of Testudo, many of them of large size, resembling the gigantic 

 tortoises of the Galapagos Islands. Sixteen species are described. In the Middle 

 Miocene of Oregon there has been found a species of Clemmys {('. saxea); 111 the 

 Upper Miocene of Kansas, Trachemys lulli. In the Vorktown beds of the Atlantic 



